The present invention relates to a sheet metal element having a hole, to a sheet metal part and to a component assembly as well as to a manufacturing method; the invention in particular concerns a sheet metal element having a hole for use in a component assembly with a sheet metal part and a rivet element.
Efforts are being made in the manufacture of cars to fasten components which are relevant to safety, such as seat fastenings, to relatively thin sheet metal parts of, for example—and without any restriction—1.0 to 1.5 mm thickness and any desired strength, for example approximately 500 MPa, and indeed in an arrangement in which the head part of the fastening element is arranged above a relatively thin sheet metal base panel and the rivet bead is arranged beneath the sheet metal base panel. This means the screwing on forces act upwardly in a perpendicular manner and attempt to pull the rivet bead through the sheet metal part. As the sheet metal part is relatively thin and for this reason does not have any pronounced local rigidity, it is difficult to find a construction which, on the one hand, can be integrated into the manufacturing process of the sheet metal base panel and, on the other hand, has a sufficient rigidity in the event of an accident in order to the avoid the tearing out of the seat anchorage.
It is the object of the present invention to provide a remedy in this case.
This is achieved in accordance with the invention in that a sheet metal element, in particular a planar sheet metal element, is provided for the local stiffening of the sheet metal part, wherein the hole margin of the sheet metal element is provided with at least one radially inwardly directed projection which forms an undercut. The sheet metal element can hereby be attached to the sheet metal part in a shape locked manner in a first manufacturing process in that sheet metal material of the sheet metal part is brought into the hole of the sheet metal element and brought into engagement with the undercut so that the sheet metal element is held captively at the sheet metal part.
In principle, it would be sufficient if only one radially inwardly directed peripheral projection, i.e. a peripheral undercut, is provided at the hole margin of the sheet metal element. However, an arrangement is preferred in which the sheet metal element and at least one undercut are provided at both sides of the plane in the hole margin with respect to a plane which is symmetrically formed perpendicular to the central longitudinal axis of the hole at half the height of the hole.
Since such a symmetrical sheet metal element is used, it is not important with which orientation the sheet metal element is attached to the sheet metal part, i.e. with which of the two end faces the sheet metal element contacts the sheet metal part. This signifies a substantial simplification of the manufacturing process since the sheet metal elements can be removed from a loose bulk of such sheet metal elements without having to ensure a particular orientation.
It is particularly preferred if a plurality of locally formed, radially inwardly directed projections which form undercuts are provided and are, for example, provided at both sides of said plane.
Such projections which form undercuts can be formed by respective wedge-shaped recesses extending in particular radially to the central longitudinal axis of the hole in an end face or in both end faces of the sheet metal element, with the greatest depth being present at the hole margin. Such wedge-shaped recesses which are reshaped into radially inwardly directed projections or noses which form undercuts can be seen from EP-B-759510. However, in the EP document, they are formed in the side wall of an end-face recess of a fastening element and not in the hole wall of a sheet metal element.
Such projections or noses which form undercuts can also be formed by at least one impression which extends in wave shape about the central longitudinal axis and which is provided in an end face of the sheet metal element adjacent to the hole margin, preferably by respective wavy impressions provided in the two end faces of the sheet metal element. Such wavy impressions which lead to the formation of radially inwardly directed projections which form undercuts are known from EP-B-957273.
It is in particular preferred if the sheet metal element has the shape of a circular metal washer. Such metal washers can be manufactured inexpensively from sheet metal material and the formation of the radially inwardly directed projections which form the undercuts can be integrated in a cost-effective manner in the process of manufacturing the metal washers.